Accounting for dynamic conditions of aerofoil flow-around while solving the problem of a helicopter main rotor trimming angles determining

Аuthors

Garipova L. I.^*, Batrakov A. S.^**, Kusyumov A. N.^***

Kazan National Research Technical University named after A.N. Tupolev, 10, Karl Marks str., Kazan, 420111, Russia

*e-mail: lyaysan_garipova@mail.ru
**e-mail: batrakov_a.c@mail.ru
***e-mail: postbox7@mail.ru

Abstract

The main rotor trimming is one of the important tasks of helicopter aerodynamics. The aim of trimming consists in determining the values of balancing angles (total and cyclic pitch angles) of the main rotor, which allows minimize longitudinal and lateral moments, as well as vibration load. A simple approach to the main rotor's balancing angles determination is based on the Blade Element Momentum Theory (BEMT), based on steady-state aerofoil aerodynamics. However, while straight and level flight the helicopter's blade sections motion bears a complex oscillated character. For this reason, aerofoil performances can differ significantly from its steady-state equivalents.

The aim of this research is numerical simulation of the oscillating NACA 23012 aerofoil flow-around to study the effect of dynamic flow conditions corresponding to a forward flight mode on the values of the main rotor trimming (total and cyclic pitch) angles. Numerical simulation was performed using HMB code (Liverpool and Glasgow universities) based on the Unsteady Reynolds averaged Navier–Stokes equations (URANS) with k‒ω SST turbulence model.

The results of study revealed that the dynamic condition leads to significant changes of the aerofoil aerodynamic characteristics and the main rotor trimming angles compared to the steady state formulation. Based on these results a correction can be employed to improve the simple BEMT approach accuracy.

Keywords:

computational aerodynamics (CAD), URANS modeling, rotor trimming angles

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